The invention relates to an apparatus for estimating a fixation point of an anthropomorphically constructed eye when gazing at an object with an eye reference point detection device with which eye reference point coordinate values of an eye reference point may be defined, with a direction of gaze detection device with which a gazing direction of the eye may be defined as a gaze direction function, and with a computer with which the fixation point of the eye may be estimated on the basis of the gaze direction function and the eye reference point coordinate values.
Such an apparatus is known from appendix 2the prior art of the final report of the project xe2x80x9cFernseh-Bildgxc3xcte bei dynamischem Blickverhaltenxe2x80x9d (Television Image Quality at Dynamic Viewing Behavior) sponsored under Sponger reference 01BK203/8 by the (German) Federal Ministry for Education, Science, Research and Technology. In the known apparatus, a rigidly mounted head position transmitter and a head position detector arranged, for instance, on a spectacle-like frame on the head of a subject are provided as an eye reference point detection device. Furthermore, the apparatus is provided with a computer for calculating the position of the head position detector relative to the head position transmitter as spatial coordinates, i.e. the distance and bearing of the head position detector with respect to the head position transmitter.
In addition, the known apparatus is provided with a gaze direction detection device which is also mounted on the frame and which is equipped for detecting a gaze directional function of an eye the fixation point of which is to be monitored on an viewing screen. In this context, the gaze direction function is derived by a method of calibration from the known fact that the position of the eye detected by two measurement values may be unambiguously assigned to a gaze direction function. Furthermore, in the prior art device a translation vector between the head position detector and an eye reference point, for instance, the center of the pupil or the center of the eye, is determined by estimation.
For estimating a fixation point on the viewing screen, the gaze direction function is scaled by the computer by relatively complex calculations, shifted by the translation vector, multiplied by a rotary matrix representing the bearing of the head relative to the head position transmitter, and corrected by the vector of the distance between the head position transmitter and the head position detector. For calculating the scaling factor, the rotary matrix representing the bearing of the head is multiplied, on the one hand, by the vector of translation between the head position detector and the eye reference point and, on the other hand, by the vectorial gaze direction function, followed by quotient formation. The two results of the multiplication are divided by one another.
A similarly constructed apparatus with a frame to be mounted to a head and supporting a head position sensor, an eye reference point detection and a gaze direction detection device, is known from the article xe2x80x9cGaze Point Direction System Allowing Head Motionxe2x80x9d by M. Lida and A. Tomono in Systems and Computers in Japan, Vol. 23, No. 6, 1992.
From U.S. Pat. No. 4,582,403, there is known an apparatus by which head movement may be compensated when determining a fixation point, by monitoring a reference point by reference point monitoring means. This apparatus is structured, in one embodiment, as an uncomfortablexe2x80x94for the subjectxe2x80x94eyeglass frame which supports a reference point detector for monitoring a reference point on an image screen as well as a device for detecting the gaze direction. In another embodiment, the reference point to be monitored is applied, for instance, to the forehead of the subject as a spot of a layer which is highly reflective in the infrared spectral range. This, however, may entail the risk of the reference point becoming separated, so that the apparatus would have to be completely calibrated again.
The task of the invention resides in the provision of an apparatus of the king mentioned above which makes it possible to monitor a fixation point on an object to be viewed quickly and without in the least disturbing the subject.
In an apparatus of the kind referred to above, this task is accomplished in accordance with the invention by the eye reference point detection device comprising a reference point detector structured as a surface detector by means of which an image of the eye may be formed within a predetermined spatial area, by the gaze direction detection device comprising a gaze direction detector structured as a surface detector which is mounted on a pivoting and tilting element which is pivotable and tiltable in two overlapping directions, whereby an image may be formed by the gaze direction detector at least of the pupil and the immediate surroundings of the pupil and whereby the pivoting and tilting element may be adjusted by a tracking unit fed by control signals from the eye reference point detection device such that upon spatial movement of the eye reference point the gaze direction detector remains aligned with the eye reference point, and by the computer comprising a compensation unit for the compensation of movement of the eye reference point which compensation unit may be fed with object coordination values associated to the object, gaze direction detector coordinate values associated with the gaze direction detector, gaze direction values associated in a gaze direction coordinate system to the gaze direction function, alignment values associated with the alignment of the gaze direction detector and eye reference point coordinate values for estimating (determining) the fixation point.
In view of the fact that for estimating the fixation point only the eye of a subject is optically monitored without being touched and that head movements are compensated for by the compensation unit by calculations of the data fed to the compensation unit and derived from the eye reference point detector and the gaze direction detector as well as the pivoting and tilting element the fixation point may be determined with relatively low mathematical complexity by executing mathematical rotation, scaling and translation steps, which in a preferred embodiment of the invention may be executed by a rotation compensation member, a scaling member and a translation compensation member.
For a highly precise monitoring of the eye reference point, the eye reference point detection device as well as the gaze direction detector are each equipped with a surface camera acting as a surface detector. To this end, the surface camera of the eye reference point detection device preferably monitors the head portion of the subject without a spatial area in which movements may be expected, whereas the surface camera of the gaze direction detection device monitors the immediate vicinity of the pupil of the eye at high resolution.
In a further embodiment the eye reference point detection device and the gaze direction detection device are provided with a common surface camera as a dual detector of high resolution, the camera being structured as an autofocus camera the autofocus positions of which may be fed to the calculator for determining the distance of the eye reference point which is preferably been derived from the pupil of the eye, from the detector plane of the dual detector. In this manner, the expenditure in terms of equipment is relatively low.